1. Field of the Invention
The present invention relates to an apparatus for driving a plasma display panel and method thereof, and more particularly, to an apparatus for driving a plasma display panel in which an image being full of life can be displayed through expansion of contrast and a gray level can be expanded, and method thereof.
2. Background of the Related Art
A plasma display panel (hereinafter, referred to as a ‘PDP’) is adapted to display an image using a visible ray generated from phosphors when the phosphors are excited by ultraviolet generated during discharging of a gas. The PDP has advantages that it is thin in thickness and light in weight and can be made large with high definition compared to a cathode ray tube (CRT) that is the greater part of the display means.
FIG. 1 is a plan view schematically illustrating a conventional plasma display panel. FIG. 2 is a detailed perspective view illustrating the structure of a cell shown in FIG. 1.
Referring to FIG. 1 and FIG. 2, a three-electrode AC surface discharge type PDP includes scan electrodes Y1 to Yn and a sustain electrodes Z which are formed on an upper substrate 10, and address electrodes X1 to Xm formed on a lower substrate 18.
A discharge cells 1 of the PDP is formed every portion where the scan electrodes Y1 to Yn, the sustain electrodes Z and the address electrodes X1 to Xm intersect. Each of the scan electrodes Y1 to Yn and the sustain electrode Z includes a transparent electrodes 12, and a metal bus electrodes 11 having a line width narrower than that of the transparent electrodes 12 and formed at one edge sides of the transparent electrodes. The transparent electrodes 12 are typically formed using indium-tin-oxide (ITO) on the upper substrate 10. The metal bus electrodes 11 is typically formed using a metal on the transparent electrodes 12 and serves to reduce a voltage drop caused by the transparent electrodes 12 having high resistance.
An upper dielectric layer 13 and a protection film 14 are laminated on the upper substrate 10 in which the scan electrodes Y1 to Yn and the sustain electrode Z are formed parallel to each other. A wall charge generated upon plasma discharge is accumulated on the upper dielectric layer 13. The protection film 14 serves to protect the electrodes Y1 to Yn and Z and the upper dielectric layer 13 from sputtering generated upon the plasma discharging and to increase efficiency of secondary electron emission. The protection film 14 is typically formed using magnesium oxide (MgO).
The address electrodes X1 to Xm are formed on the lower substrate 18 in the direction in which they intersect the scan electrodes Y1 to Yn and the sustain electrode Z. A lower dielectric layer 17 and barrier ribs 15 are formed on the lower substrate 18. A phosphor layer 16 is formed on the lower dielectric layer 17 and the barrier ribs 15. The barrier ribs 15 have the form of stripe or lattice and physically separate discharge cells, thus shielding electrical and optical interference among neighboring discharge cells 1. The phosphor layer 16 is excited and light-emitted by ultraviolet rays generated upon plasma discharge to generate any one visible light of red, green and blue lights.
An inert mixed gas for a discharge such as He+Xe, Ne+Xe or He+Ne+Xe is injected into discharge spaces of the discharge cells defined between the upper substrate 10 and the barrier ribs 15 and the lower substrate 18 and the barrier ribs 15.
In this PDP, in order to implement the gray level of an image, one frame is divided into several sub fields having different numbers of emission and is then driven in time division. Each of the sub fields is divided into a reset period for generating discharging uniformly, an address period for selecting a discharge cell, and a sustain period for implementing the gray level depending on the number of discharging. For example, if a picture is to be represented using 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight sub fields. Also, each of the eight sub fields is divided into a reset period, an address period and a sustain period. In the above, the reset period and the address period of each of the sub fields are the same every sub fields, whereas the sustain period and the number of discharging thereof increase in the ratio of 2n(n=0, 1, 2, 3, 4, 5, 6, 7) in each of the sub fields in proportion to the number of a sustain pulse. Since the sustain period is different in each of the sub fields as such, it is possible to implement the gray level of an image.
FIG. 3 is a block diagram showing a conventional apparatus for driving a plasma display panel.
Referring to FIG. 3, the conventional apparatus for driving the PDP includes a gain control unit 32, an error diffusion unit 33 and a sub field mapping unit 34 all of which are connected between a first inverse gamma control unit 31A and a data alignment unit 35, and an APL calculator 36 connected between a second inverse gamma control unit 31B and a waveform generator 37.
The first and second inverse gamma correction units 31A and 31B perform inverse gamma correction for digital video data (RGB) received from an input line 30 to linearly convert brightness of a gray level value of an image signal.
The gain control unit 32 compensates for color temperature by adjusting an effective gain by each data of red, green and blue.
The error diffusion unit 33 finely controls a brightness value by diffusing quantization error of digital video data (RGB) received from the gain control unit 32 to adjacent cells. In the above, a gray level of data that passes through the error diffusion unit 33 is expanded finely.
The sub field mapping unit 34 serves to map the data received from the error diffusion unit 33 to a sub field pattern stored by the bit and supply the mapping data to the data alignment unit 35.
The data alignment unit 35 supplies digital video data received from the sub field mapping unit 34 to a data driving circuit of the panel 38. The data driving circuit is connected to data electrodes of the panel 38 and serves to latch data received from the data alignment unit 35 by one horizontal line and then supply the latched data to the data electrodes of the panel 38 in one horizontal period unit.
The APL calculator 36 calculates average brightness for digital video data (RGB) received from the second inverse gamma correction unit 31B in one screen unit, i.e., an average picture level (hereinafter, referred to as ‘APL’) and outputs information on the number of a sustain pulse corresponding to the calculated APL.
The waveform generator 37 generates a timing control signal in response to the information on the number of the sustain pulse from the APL calculator 36 and then supplies a timing control signal to a scan driving circuit and a sustain driving circuit (not shown). The scan driving circuit and the sustain driving circuit supplies the sustain pulse to the scan electrodes and the sustain electrodes of the panel 38 during the sustain period in response to the timing control signal received from the waveform generator 37.
Such a conventional PDP expands the gray level minutely using the error diffusion unit 33. If the gray level is expanded using the error diffusion unit 33 as such, there is a problem that the picture quality is lowered because an error diffusion pattern is shown in data of a predetermined pattern.
Furthermore, in order to display an image being more full of life in the conventional PDP, contrast of a gray level must be clear. In the conventional PDP, however, it is difficult to display an image being full of life since there is no method for expanding contrast of data.